Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$34.88	8.641%	$37.894	$37.89	$37.90	$37.90
Purchase #2	$237.30	13.252%	$268.747	$268.75	$268.75	$268.70
Purchase #3	$229.45	12.704%	$258.5993	$258.60	$258.60	$258.60
Purchase #4	$157.44	9.559%	$172.4897	$172.49	$172.50	$172.50
Purchase #5	$244.83	4.577%	$256.0359	$256.04	$256.05	$256.00
Purchase #6	$44.96	13.513%	$51.0354	$51.04	$51.05	$51.00
Purchase #7	$97.60	6.309%	$103.7576	$103.76	$103.75	$103.80
7 purchase totals =	$1,046.46		$1,148.5589	$1,148.57	$1,148.60	$1,148.50